1. Field of the Invention
This invention relates to molded case circuit breakers, and more particularly, to a molded case circuit breaker provided with ground fault protection and signaling switches incorporated into a modular unit insertable into the circuit breaker molded case.
2. Background Information
Molded case circuit breakers for light to medium industrial and commercial applications have a case molded from an electrically insulative resin. Such circuit breakers can be single pole or multi-pole. In the latter case, the multiple poles are housed in side-by-side compartments formed in the molded case. Each pole has a trip device which actuates a common trip bar in response to over current conditions. The common trip bar unlatches a latchable spring powered operating mechanism which through a common crossbar opens the contacts in each pole to interrupt all phases of load current.
It is common to provide ground fault protection in the smaller residential circuit breakers also known as miniature circuit breakers. A common ground fault circuit used in such applications includes a toroidal coil for differential current sensing. Both the line and neutral leads are passed through the sensing coil. Normally the currents in the leads are equal and opposite, but a ground fault causes an imbalance which generates a signal in the winding of the toroidal coil. This signal is processed, typically by circuitry implemented on a printed circuit board, and energizes a solenoid which actuates the trip mechanism. The purpose of the ground fault detector in residential circuit breakers is to protect persons from electrical shocks and the accepted level for tripping is 5 ma of ground fault current.
In industrial applications, ground fault detection is provided to protect the equipment serviced by the circuit breakers. The threshold for protection in these applications is typically 30 ma. Such equipment protection has not been provided in molded case circuit breakers in this country, although it is in use in similar circuit breakers in Europe. There is an interest now in providing similar capability in domestic molded case circuit breakers.
It is common to provide remote signalling switches in molded case circuit breakers. Typically, the switches are of two types: auxiliary switches which provide an indication of the state of the contacts, open or closed, and bell alarms which provide a signal indicating that the circuit breaker has tripped. Such switches are commonly separately mounted inside the circuit breaker molded case.
There is a need therefore for a molded case circuit breaker having ground fault protection and in particular ground fault protection for equipment.
There is a related need for ground fault protection which can be added to a molded case circuit breaker with minimum modification of the existing breaker design.
There is also a need for such ground fault protection which can be selectively provided without undue additional manufacturing costs or time.
There is a further need for such ground fault protection which can be implemented easily together with remote signalling switches such as auxiliary switches and bell alarms.
There is an additional need for an arrangement which is flexible enough to allow for varied customer requirements for ground fault protection and remote signaling.